Electric wave transmission system



March 29, ALToVs KY ELECTRIC WAVE TRANSMISSION SYSTEM Filed March 10, 1945 4 Sheets-Sheet 1 I/ I/ I M/rze [RAMA 0E7. ZEAMP.

ffCA/VNEE I 1 1 I MODULA 7'02 7244 3407 me. 0.5T. L .E'A MP.

SWEEP GEN.

IN V EN TOR. V4 mum/e 44 7'0 vsxr March 29, 1949. ALTOVSKY 2,465,341

ELECTRIC WAVE TRANSMISSION SYSTEM Filed March 10, 1943 4 Sheets-Sheet 2 IN V EN TOR.

March 29,

Filed March 19 v. ALTOVSKY ELECTRIC WAVE TRANSMISSION SYSTEM 10, 1943 4 Sheets-Sheet 5 IN V EN TOR.

March 29, 1949. v. ALTOVSKY 2,465,341

ELECTRIC WAVE TRANSMISSION SYSTEM Filed March 10, 1945 4 Sheets-Sheet 4 mace/mm roe SWEEP saw.

14 TTOR/VE Y Patented Mar. 29, 1949 ELECTRI-C WAVE- TRAN SMIS SION SYSTEM Vladimir Altovsky; Paris, France, assignor to International-Standard Electric Gorporation, New York, N. Y ur-corporation of Delaware Application-MarclilO, 1943,.Serial No. 478,698 In FranceFebruary 8, 1941 Section :1, Publicilzaw 690, August 8, 1946 Patent expires February 8, 1961 5 Claims; 1

The present invention relates to electric wave;

transmission systems and particularly but not, exclusively to-wave transmission systems employing very high frequencies, such as decimeter or centimeter waves. In. the conventional transmissionsystems that use decimeter or centimeter waves, the reception, of these waves calls for a=very great degree of fre.-- quency stability on the part of the. receivingequip ment, which stability must be all the greatenaccording as the carrier frequency is relatively higher.

In these systems, as a matter of fact, the. transmission wave always has frequency variations of an importance that usually becometroublesome for reception.purposes,.whether itis. a question of awave. modulated in amplitude or. by impulses with a parasitic frequency modulation, or else. of;. awave. modulated as to frequency, whosedepth of modulation cannot be reducedlto a sufiiciently low value. Besides, the average. value ofithe. trans-- mission frequency may have variations that pro-; ceed from various causes such as the instability.- ofthe sources of supply, which is a preponderant factor for oscillators of'tlie type havinga' transitl time of the electrons that is appreciable with respect to the period of oscillation. This latter drawback is still worseat' thereceivin'g end'in the; case of superheterodyne' receivers in respect to changes brought about in the valueofth'e' variations'of the local oscillator: Thesizeof' these'frequency-variations can be seen more-clearly when one considers that, e. g; for a wave-of 3000 mega cycles, a stability of the-order'of- 1 permits-the" absolute variations of frequency to be o'fthe or der of 3-megacycles Asa result ofthis, systems transmitting by means of centimeter or'decimeter: waves with useof the ordinary methods,.require complex stabilization equipment both at the transmitting and the receivi'ngendsrof such .systems.

At the-receiving end also,.the tuningzof'the rea ceiver to the transmissioniwavelength requiresiai degreeof precision that may prove tobe a seriousdrawback for certain uses.

This invention includes among its objects the: provision of very high frequency transmission: systems which will no longer require such extreme. conditions of stability and practically may allow one to dispense with additional stabilizing equip.- ment' both at the transmitting. and receiving ends,,

and which furthermore do not require precise,

tuning of the, receiver. to! the transmission. wave.-. length.

Another object. of the invention consists in the necessarily high with regard to stability, so-that this makes it possible to construct these systems with regular equipment possessing small dimensions, if. so desired.

Another object of the invention isthe providing. of. receivers that are particularly adapted for de-- tecting transmissions of unknown wavelengths. even when such transmissions are of unstable frequency.

Still another object of the. invention is the pro viding of high frequency transmission systems that permit use at the receiving endof simple cir-- cuits that do not require change and stabilization of frequencies, nor the complexapparatus needed; for such stabilization.

A high frequency transmission system that incorporates features of' the invention comprises, either at the transmitting or receiving ends,. means for producing a frequency scanning of the. transmitted wave or of the beat of the wavereceived together with an oscillation. proceeding. from'a local oscillator, this scanning being'rapid, with respect to the modulation of this wave andof' sufiicient width to cover possible undesirable variations of. the frequency.

According toone embodiment of the invention,

' this rapid frequency scanning is introduced at'the receiving end by submitting the local oscillator of a superheterodyne to such a frequency scanningf that the frequency of this local oscillator will fluctuate between two" limits the difference be.- tween which is established as greater than the: sum of the assumed variations of the'frequency of the incident wave and of the frequency of the local oscillator itself, consideredwithout scanning, the scanning frequency being selected so as to be. comparatively great with respect to the modulation frequency of the incident wave.

According to another embodiment of the in vention, this rapid frequency scanning is introduced at the transmitting end by subjecting the oscillator of the transmitter to a frequency scanning of such value that its frequency fluctuates between two limits the difierence between which is determined as greater than the sum of the possible variations of the transmitter, considered withouti scanning, and of. the possible variations of the" tuning frequency of the receiver or receivers, the scanning frequency being selected to belarge with respect to the frequency of the modulation or modulations-ofthe wave that'it is desired to trans mit. The receiver may then be of the frequency changing type or not, as desired.

According to another form of the invention, a transmission system for very high frequencies, that permits reception of a wave with an apparent amplitude modulation of almost 100 at frequencies for which such a depth of modulation is particularl difficult if not impossible to obtain with conventional amplitude modulation circuits, comprises a transmitter having frequency modulation and rapid quadratic course frequency scanning of the above described kind superposed, and an ordinary receiver for amplitude modulated waves.

According to another variation of the invention, a frequency modulated wave is received by a receiver which comprises a frequency scanning that permits restoration of the modulation transported by the wave together with an arrangement provided for receiving an amplitude modulated wave.

According to still another variation of the invention, there is provided a receiver that makes it possible to locate operating stations and to receive a transmission of unknown wavelength comprising a superheterodyne circuit that has its local oscillator controlled by means of frequency scanning of great width of variations for the automatic detection of the transmission to be received, and a discrimination circuit for automatic control of the frequency in order to automatically narrow the width of the variations of the frequency scanning, under control of the received signals, to the useful value for obtaining efficient reception of the signals.

These points and characteristic features of the invention, as well as others, will be explained in detail in the following description with reference to the appended drawings, in which:

Fig. 1 is a schematic view of one example of a receiving circuit that incorporates this invention;

' Figs. 2 to 7 inclusive show graphs used for explaining certain features of the invention in connection with various types of modulation;

Fig. 8 illustrates schematically a transmission system which incorporates features of the invention and in which the transmitter circuit is frequency scanned;

Fig. 9 illustrates schematically one example of an embodiment of the system shown in Fig. 8;

Fig. 10 is a schematic view of one example of an embodiment of a frequency modulated transmitter that incorporates features of the invention; and

I Fig. 11 illustrates schematically one example of a receiver that incorporates features of the invention and is particularly suitable for the detection and reception of a transmission of unknown wavelengths.

In order to simplify the explanation, there will first be explained in detail the general mode of operation of systems that incorporate features of the invention when it is applied to a system in which the transmitter is of any conventional type and the transmission is accordingly subjected to the disturbances mentioned at the beginning of this description, but in which the receiver is one made according to this invention. This receiver is, for example, a superheterodyne receiver like the one shown schematically in Fig. 1.

In this Fig. 1, a wave received on the receivin antenna I is brought into the mixing stage 2 to which the local oscillation is supplied by an oscillator 3. The output of this mixing stage 2 is then transmitted in the usual Way to an intermediate frequency amplifier 4 followed by a detector circuit 5 and a low frequency amplifier 6. The output circuits (e. g. to feed loud speakers) are not shown at the output of the low frequency amplifier 6.

According to one feature of the invention, the local oscillator 3 is subjected to a frequency scanning that is provided by a scanning circuit 1. This scanning is provided in such a way that the frequency of the local oscillator 3 fluctuates between two limits, Fh-l-fh and Fn)n the frequency excursion having an amplitude greater than the sum of all the assumed variations of the frequency of the incident wave and of the frequency of the local oscillator, considered without scanning. The scanning frequency is selected so as to be of a high value with respect to the modulation frequency carried by the incident wave.

The mean value Fh of the frequency of the local oscillator 3 is adjusted approximately so that the beat frequency produced with the mean value Fl of the incident wave may correspond to the intermediate frequency of the receiver.

During an excursion of the frequency of the local oscillator 3. e. g. from Fnfh to Fh-l-fh, the momentary value of the beat with the incident wave will vary by 2Fn during this excursion, as is shown in the curve of the frequencies of Fig. 2. For a certain interval of time it will be in the width of the pass band of the intermediate frequency amplifier 4, and this will cause a brief current to pass in the detector 5. m in Fig. 2 indicates the pass band of the amplifier 4 centered on the axis w-x' that corresponds to the intermediate frequency.

This phenomenon will occur again at each semialternation of the frequency variation as a function of the time.

During the frequency variations of the local oscillator, the intermediate frequency amplifier 4 is made active for portions (11b1, azbz, etc. that have frequencies corresponding to its band width, thus generating the wave trains as shown in Fig. 2 of the drawing underneath the frequency variation curve. These semi-amplitude wave trainsX, after detection in the detector 5, furnish elementary current elements or impulses. When the frequency of the incident wave varies, e. g. diminishes, the beat displays the value m on segments a'1b'1, etc. which are, for example, displaced on the scanning curve toward the lower frequencies. All the frequency variations, either of the incident wave or of the mean value of the local oscillator are represented by a similar displacement of the useful regions, which rise or drop on the scanning curve as they give beat frequengies lying in the band pass region of amplifier An amplitude modulated carrier wave is furthermore capable of having undesirable frequency variations due to the modulation, or any other cause. The useful portion A'1Bi of the scanning curve is selected to be linear or approximately linear. Since the scanning frequency has been selected to be large with respect to the amplitude modulation frequency, there are produced during any given period of the modulation a great number of elementary impulses of the kind defined above and shown in Fig. 2. Each of these impulses has as its amplitude that of the incident wave under consideration at the moment. The envelope of the amplitudes of the elementary impulses consequently reproduces the useful signal. Fig. 3 shows such elementary impulses rectilled with variable amplitude X, of duration T and of spacing in time 0:, 0:, etc.

Frequency variations of the incident wave, if there are any, and also the variations of the local oscillator other than those due to the scanning, result in modifying the relative distances at, a of the impulses with respect to each other.

The duration T of each impulse depends on the slope of the scannin curve in the useful regions (11271. This slope will bedesignated by p and it is equal to if dt We have m being the band width of the intermediate frequency amplifier.

If the scanning curve is substantially linear in the useful portion A'1B1 the duration of the impulses will be independent of the variations of frequency, and the envelope of the amplitudes will reproduce without distortion tl e signal carried by the modulation of the incident wave.

The scanning period may comprise two symmetrical or asymmetrical curve parts. By way of illustration, Figs. la, 4b and 4c show some examples of scanning curves that it is possible to obtain with known circuits and that can be used to fluctuate the frequency of the local oscillator 3 (Fig. l) for the reception of signals modulated in amplitude.

Fig. 4a shows a sinusoidal scanning, the useful parts being indicated by heavy dashes. Two equal impulses per period are consequently transmitted to the amplifier 4.

Fig. ib shows a symmetrical sawtooth scanning. There are also two equal impulses per period transmitted to the amplifier 4.

Fig. 4c shows an asymmetrical sawtooth scanning. The two impulses of the period are unequal, and one of them may become negligible owing to its shortness.

In the case of a frequency modulated signal, the carrier wave may have undesirable variations of the mean value of the band of modulation frequencies, as well as parasitic variations of amplitude.

The useful portion A1B'1 of the scanning curve should then have a quadratic course. Such a curve is shown in Fig. 6c and means for producing it are well-known in the cathode ray tube art. For example, a condenser charged through a resistance until the potential suddenly breaks down a gas discharge tube, will yield this form of curve in reverse and an electronic amplifier will reverse the phase of the curve. It is thought unnecessary to describe such well-known circuits in detail. It can be seen that, according to Fig. 2, the width of an impulse, i. e. its duration, is inversely proportional to the slope of the scanning curve on the useful portion. With a scanning curve of quadratic course:

i being the time, f the frequency, and K a coefficient, we have:

The duration or an impulse is proportional to 6 the variation of the frequency f of the incident wave. When the incident wave is frequency modulated, the width of the impulses is variable in accordance with the modulation, and this again permits restoration of the signal after detection. This can clearly be seen by considering the frequency modulation curve as a function of the time in Fig. 5a and the curve of the amplitudes of the corresponding detected impulses shown in Fig. 5b. The frequency modulation of the incident wave is thus detected with an amplitude modulation detection device; everything takes place as if the frequency modulation had been transformed by the scanning into amplitude modulation. In order to avoid the influence of the variations of amplitude of the incident wave, a voltage limiter to insure impulses of constant amplitude may be inserted in front of the detector 5 (Fig. 1), if sodesired.

The variations of the mean value of the fre quency of the incident wave shift the mean point of operation on the scanning curve in the manner described for Fig. 2, without presenting any other drawback for reception of the signal, if this curve be quadratic.

The scanning curve may comprise two symmetrical or asymmetrical .half-periods. Figs. 6a to 60 give some examples illustrative of scanning curves that can be used in the case of a transmission by frequency modulation.

In the ca-se when the incident wave is modulated by impulses, from the standpoint of reception the wave may be considered as being modulated in amplitude with a very great depth of modulation, as is shown in Fig. 7a. The method of reception by rapidfrequency scanning in accordance with the present invention is particularly suitable for the case of wavesmodulated by impulses, owing to the fact that the momentary high power employed in this kind of transmission generally makes it difficult to produce stabilized operating voltages at the transmitter. One example of a suitable manner of scanning such a wave is shown in Fig. 7b, the

' period of this asymmetric sawtooth scanning being slightly greater than the duration of an impulse and its frequency being synchronized to a multiple of the frequency of the impulses. At the receiving end, the signals will then have shapes similar to those indicated in Fig. '70.

A reception method such as that provided in the present invention consequently permits effective reception of wavesmodulated by amplitude, frequency or impulses, without requiring special arrangements for insuring the frequency stability of the transmitting or receiving circuits. It is therefore particularly suitable for ultra short waves, of decimeter or centimeter length, in which the requirement of good stabilization causes considerable difficulty in construction and use. As previously described and explained, the undesirable variations of frequency or of amplitude are practically without effect on the receiving circuit.

Furthermore, adjustment of the receiver to the transmission wavelength no longer requires extreme precision, since it becomes possible to allow for the error of adjustment by lengthening of the scanning and to be satisfied with a rough adjustment of the receiver'to the wavelength to be received.

Instead of using frequency scanning at the receiving end, it may be advantageous to use it at the transmitting end, and, according to certain of its features, the invention consequently provides systems like that shown schematically in Fig. 8. This frequency scanning used in a transmitter permits simplification of the circuits at the receiving end and even in certain cases makes it possible to use circuits without change of frequency at the receiving end, e. g. to use circuits of the reaction and super-reaction type instead of having to use superheterodyne receiver circuits.

In the system of transmission shown in Fig. 8, the transmitter 8 is modulated with the desired form of modulation, by an effective source of modulation 9. At the same time, the frequency of the wave to be transmitted undergoes a frequency scanning of suitable type according to the kind of modulation used, which scanning is produced by a sweep circuit l'0. This frequency scanning has the same special features as those described above for frequency scanning at the receiving end, i. e. the scanning frequency is selected so as to be great with respect to the modulation frequency of the wave to be transmitted, and the difference between the limit frequencies of the scanning is greater than the sum of the possible variations of the transmitter, considered without scanning, and possible variations of the tuning frequency of the receiver or receivers.

The wave thus modulated and of variable frequency according to the type of scanning used is transmitted by the antenna II and is then received, for example, by the antenna l2 of a simple reeciver which comprises a detector circuit [3 followed by a low frequency amplifier M which latter may feed a device for reproduction of the signals (not shown).

One example of an embodiment of a system of this kind is shown schematically in Fig. 9. The transmitter consists of an electron velocity modulated transmitting tube l5 coupled to a transmitting antenna Hi. This tube is shown by way of example as comprising a cathode l1 having any suitable cathode heating means (not shown), a control grid l8, two resonant cavities l9 and I9 which play the parts of grouper or modulator and of collector or receiver respectively according to the known art of velocity modulation tubes, and a collecting electrode 20. It may be, for example, modulated in amplitude by the control grid it, as shown by the graph 2 I, a conventional biasing circuit being indicated at 22, and it may be subjected to a frequency scanning as described above and shown at 23 by variation of the high voltage excitation, the source of which is diagrammatically shown at 24.

The wave thus modulated in amplitude and of variable frequency in accordance with the frequency scanning 23 is transmitted by the antenna I6 and is received at the receiving end by antenna 25 and is transmitted to a resonant cavity diode detector 26. The received impulse reproduces the useful modulation at the terminals of resistance 21. A condenser 28 in shunt with the resistance 21 provides, in cooperation with resistance 21, a time constant that permits of withdrawing practically the maximum voltage of the impulses at the terminals of resistance 21 but without injuriously affecting the correct reproduction of the highest frequencies of the useful modulation.

The use in the receiver of a resonant cavity diode detector is particularly effective because this makes it possible to utilize advantageously the properties of the circuits having very high excess voltage coefficients that are well known the field of ultra short waves. of decimeter or centimeter length, whereas a conventionaldiode detector would have its operation rapidly limited by the transit time of the electrons at these frequencies when the voltage would drop.

For normal transmissions, however, under continuous working conditions, the use of very high excess voltage coeflicients would impose conditions of stability too severe to make it suitable to consider employing them. In a transmission system that incorporates features of the invenwhich the transmitter makes simultaneous use.

of a modulation by impulses and a frequency scanning in accordance with certain features of this invention, as also herein described.

The detection provided by the diode detector as shown, the electric circuit of which consists of the resonant chamber 29, consequently insures, without any equipment for stabilization or change of frequency, correct reception of the signals which are then amplified in a low frequency amplifier (not shown), the input of which is taken from the detector at 30, as shown.

Fig. 10 illustrates one example of a frequency modulated oscillator that makes it possible to provide, according to features of the invention, a transmission system in which the transmitter is frequency modulated and the receiver is of a conventional type for receiving waves modulated in amplitude, with the requirements of frequency stability eliminated at both transmitter and receiver.

The oscillator shown in the drawing comprises a magnetron 3| with split anodes 32 and 33 which coaxially surround a rectilinear filament 34. This particular type of tube is, of course, only shown here as one example of a short wave oscillator. The magnetic field is indicated with an arrow, by its direction 35. This oscillator is subjected to a double frequency modulation, the one indicated at 36 being the useful frequency modulation that furnishes the desired signals and the other indicated at 31 being a frequency scanning of quadratic course similar to the scanning indicated in Fig. 60. This quadratic course scanning possesses the above mentioned qualities of rapidity and extent, and it acts upon the magnetron by variation of the high voltage 38 thereof. The useful modulation 36 is applied to the two plates 32 and 33.

The effect of the quadratic frequency scanning is to transform the frequency modulation into amplitude modulation for purposes of reception. The effective depth of this new kind of amplitude modulation may reach which has hitherto been practically unobtainable with known types of amplitude modulation circuits for ultra short waves, e. g. for those of centimeter length. Indeed, by referring to Figs. 5a and 5b, it can be seen that the relative lengths of the various impulses produced by the combined action of a modulation sinusoidal and a quadratic course scanning may be considerably difierent and be actually expressed by variations comparable to variations of amplitude, having a depth amounting to practically 100%.

According to another feature of the invention, the transmission systems provided in the present invention likewise permit reception of a transmission having an unknown wavelength, by using a receiver provided with frequency scanning means, as previously described and explained herein. One example of such a receiver is shown schematically in Fig. 11 and, according to one embodiment of the invention, it uses a positive griditube subjected to a frequency scanning.

In Fig. 11, the local oscillator 39 of the positive grid type, having the elements thereof indicated in the conventional manner, the circuit of which comprises the high voltage 40 and the bias polarization source 4|, is frequency controlledby variation of its anod voltage at the terminals 42 by means of a scanning circuit 43 that produces a rapid frequency scanning, e. g. of sawtooth form, as indicated by the graph.

A mixing diode detector 44 with tuning circuit 45 is actuated on the one hand by th signals picked up by the antenna 45 and transmitted to the detector by a transmission line 41 of any suitable type and, on the other hand, is excited by means of an inductive coupling 48, indicated by an arrow, to the output of the frequency scanning positive grid oscillator 39. The intermediate frequency beats that are thereby produced, are sent into an intermediate frequency amplifier 49, which is followed by a detector 50 and a low frequency amplifier 5|. The output device or devices are not shown at the output of the low frequency amplifier 5|, but may be of any suitable type as known in the art.

A system of automatic adjustment of the frequency is provided so as to react directly on the local oscillator 39. This system, which consists of a discrimination circuit 52, is slow acting with respect to the frequencies of the useful modulation and corrects only the frequency variations, in a manner well known in the art. The frequency scanning provided by the device 43 is rapid with respect to the useful modulation frequencies and acts by super-position on the automatic control action of circuit 52, as this not only permits automatic finding of the station to be received on account of the great extent or width of the scanning but also avoids the drawback of frequency modulation at the frequency of the useful signal.

In the above described examples, it is evident that the circuits and arrangements that have been shown do not call for highly detailed description, since they are, in themselves, all well known in the art.

It is likewise evident that the invention is not limited to the example of embodiments shown and described but is, on the contrary, capable of numerous modifications and adaptations without departing from its scope.

What is claimed is:

1. A signal energy transmission system including transmitting apparatus for frequencies having a wave length of the order of decimeters or shorter comprising means for producing an electron beam, a plurality of tuned means and an anode electrode in the path of said beam, means to apply signal modulation to said beam, means to couple the tuned means to produce oscillation and means to apply a varying voltage to the anode electrode whereby said oscillations are varied in frequency, said varying voltage having 5 such a value that the oscillations vary in frequency through a band of frequencies great enough to include all frequencies over which said apparatus may sufier frequency instability in said order of frequencies together with the sig- 10 nal modulation and at a high rate relative to said signal modulation, and receiving means comprising a cavity resonator diode operating in a relatively fixed frequency band of width comparable to that of the modulated signal considered without said wave variation for demodulating said signal.

2. A signal energy transmission system according to claim 1, wherein said tuned means comprises successive cavity resonators.

3. A signal energy transmission system according to claim 1, in which said means to apply signal modulation to said beam includes a grid in the path of said beam and means to apply the signal voltage thereto.

. 4. A signal energy transmission system according to claim 1, wherein said means for varying the oscillations produces a frequency band of saw-tooth wave form.

5. A signal energy transmission system according to claim 1, wherein the said cavity resonator diode is connected for direct detection.

VLADIMIR ALTOVSKY.

REFERENCES CITED The following references are of record in the file of this patent:

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